In the manufacture of semiconductor devices, chips embodying integrated circuits (ICs) are often contained in a package having a plurality of external leads extending therefrom. When such packaged devices are mounted to a circuit board for end use, it has been found advantageous to have the leads of the device aligned in one or more rows to suit a typical board layout. In a currently popular, lineally leaded package for ICs, the leads are aligned in two rows causing the device to be referred to as a dual inline package (DIP). Even in high volumes of production, most IC manufacturers test each circuit before delivery and it is therefore desirable to test such circuits rapidly and reliably.
In testing ICs, it is customary to contact each external lead with two related contacts, sometimes called a Kelvin pair. The primary purpose of using two contacts on each lead is to accurately measure a small voltage drop across an IC while such circuit is being tested. Typically, at a first contact made on a lead for such testing, a localized voltage drop is experienced which could affect measurement of circuit voltages. However, at a second contact made on the same lead, any localized voltage drop is typically negligible because the current flowing therethrough is negligible and better measurements are obtainable. The problem is to make proper contact of the Kelvin pair to a lead and to simultaneously make similar contact of similar pairs to each respective lead of the device to be tested.
Conventionally, DIPs have had from about 16 to about 20 external leads extending therefrom, although IC packages containing up to 40 leads are now not unusual. In testing such 40 leaded DIPs, it is mechanically challenging to simultaneously flex 80 spring tempered conductors of a test head toward 40 leads of a DIP and to effectively make 80 good, simultaneous contacts thereto. Nevertheless, this procedure must be repeated many times each minute to test such DIPs rapidly and reliably.
For a typical prior testing apparatus, the contacts were fabricated in pairs, separately from all other pairs. Such separate pairs were then aligned in two rows, spaced apart sufficiently to permit a DIP to be indexed between the rows and to permit reasonable clearances thereto. Once the DIP is in position, two opposing push rods act in unison to simultaneously flex all contacts in each row toward and against the leads of the DIP. It will be appreciated that uniformity in the performance of the contact pairs is important in achieving simultaneous and uniform contact and therefore good testing.
Typically in such conventional apparatus, the contact pairs are aligned in the rows by shimming and clamping base insulators which hold the contacts in a test fixture, a procedure which takes much time and patience. Since the pairs are very expensive and because they have a wide disparity of service life, it is customary to replace each pair separately as it wears out. Such replacement disturbs the shimming and alignment of adjacent pairs in the row, thereby requiring costly labor and down time to realign the pairs. It is therefore desirable to improve the apparatus for testing DIPs so costly labor and down time can be minimized.